WASHINGTON — The F.B.I. has concluded that there was little its agents could have done to prevent the Boston Marathon bombings, according to law enforcement officials, rejecting criticism that it could have better monitored one of the suspects before the attack.

That conclusion is based on several internal reviews that examined how the bureau handled a request from a Russian intelligence agency in 2011 to investigate whether one of the suspects, Tamerlan Tsarnaev, had been radicalized during his time in the United States.

Mr. Tsarnaev, who along with his brother, Dzhokhar, came to the United States about a decade ago from the Russian republic of Dagestan, was killed during a shootout with the police four days after he and his brother detonated two bombs at the finish line of the marathon, killing 3 people and injuring more than 200, the authorities say.

Members of Congress have contended that the F.B.I. should have done a more extensive investigation of Mr. Tsarnaev in response to the Russian request. And they have said the bureau should have followed up with Mr. Tsarnaev after he returned from a trip to Russia in 2012.

But F.B.I. officials have concluded that the agents who conducted the investigation and ultimately told the Russians that there was no evidence that Mr. Tsarnaev had become radicalized were constrained from conducting a more extensive investigation because of federal laws and Justice Department protocols. Agents cannot use surveillance tools like wiretapping for the type of investigation they were conducting.

The officials have also determined that had the agents known that Mr. Tsarnaev had traveled to Russia for months in 2012, they probably would not have investigated him again because there was no new evidence that he had become radicalized.

The most recent criticism of the F.B.I. from Congress came on Wednesday, when Representative William Keating, Democrat of Massachusetts, sent a letter to James B. Comey, the incoming F.B.I. director. In the letter, Mr. Keating demanded that the bureau respond to several questions about its actions in the years before the attack.

“What I am looking to do is identify our security shortcomings and change them,” Mr. Keating said in the letter. “Without forthright information from the F.B.I., we are prevented from taking the critical steps needed to protect the American public.”

Mr. Keating said in a telephone interview that the F.B.I. had refused three requests by the House Homeland Security Committee to testify about the attack, citing an investigation. “Until they give us facts that we can review as an independent branch of government, I don’t think that’s particularly useful what they think,” he said of the F.B.I.’s conclusion that there was little it could do to stop the attacks.

F.B.I. officials often review how the bureau has handled investigations after attacks, and they have sometimes acknowledged mistakes.

After the 2009 Fort Hood shooting, which left 13 people dead, the criticism of the F.B.I. was far more pointed. The F.B.I. appointed one of its former directors, William H. Webster, to conduct a formal review into how the bureau handled its investigation of the gunman before and after the attack.

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That review, which found that the bureau had made mistakes in handling intelligence information, resulted in recommendations for changes that the F.B.I. could make to its information sharing and training.

In the Boston case, the F.B.I. has no plans to appoint an investigator to examine its procedures. But inspectors general from four federal agencies, including the Justice Department, said they would be working together on their own investigation into how the government handled intelligence before the attack. The F.B.I. has been cooperating with the inspectors general by giving them investigative files and the opportunity to interview agents.

A spokesman for the F.B.I. declined to comment, citing the investigation by the inspectors general.

The F.B.I. first learned that Mr. Tsarnaev may have been radicalized in early 2011, when Russian intelligence officials sent a letter to F.B.I. agents stationed at the American Embassy in Moscow. The letter, according to the F.B.I., said that “he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel” to Russia to join a terrorist group.

The letter prompted the F.B.I. to open an investigation in Boston. As part of that inquiry, counterterrorism agents looked at Mr. Tsarnaev’s criminal, education and Internet histories and found little that made them suspicious.

That April, F.B.I. agents interviewed Mr. Tsarnaev’s parents, and shortly thereafter they interviewed him and found nothing suspicious. Two months later, the agents closed the investigation of Mr. Tsarnaev, determining that they could not find any information linking Mr. Tsarnaev to extremists or extremist beliefs.

The F.B.I. went back to the Russian intelligence service to request more information on Mr. Tsarnaev but was not sent anything, according to bureau officials. The F.B.I. made another request in 2011, but the Russians once again did not send any information.

Mr. Tsarnaev did not show up again on the F.B.I.’s radar until four days after the bombings, when his body was identified at a Boston-area hospital after the shootout. Several hours later, the F.B.I. discovered in its files that it had investigated him in 2011.

It is unclear whether the F.B.I. was informed by the Department of Homeland Security in 2012 that Mr. Tsarnaev had returned from his trip to Russia.

Shortly after realizing that there was no formal way of notifying agents that someone they had investigated may have been traveling outside the United States, the F.B.I. and the Department of Homeland Security changed their procedures so that agents are given written notification that someone they investigated had traveled abroad.

While these changes are likely to streamline information sharing in the future, one law enforcement official said that “it’s fair to say that had these adjustments been in existence before the attacks, the outcome would likely not have been any different.”

Eric Schmitt contributed reporting.

A version of this article appears in print on August 2, 2013, on Page A13 of the New York edition with the headline: F.B.I. Said to Find It Could Not Have Averted Boston Attack. Order Reprints|Today's Paper|Subscribe